Abstract/Summary

Viral production was determined in the sub-Antarctic zone (SAZ) to the southwest and southeast of Tasmania and in the Polar Frontal zone (PFZ) of the Australian sector of the Southern Ocean during Austral summer (January–February 2007). Concentrations of viruses were the lowest (6.6 × 109 particles l−1) in the PFZ and the highest (2.1 × 1010 particles l−1) in the eastern SAZ where nutrient input from the East Australian Current (EAC) sustained higher concentrations of bacteria and bacterial production relative to the west. Rates of viral production in the PFZ (1.8 × 1010 viruses l−1 day−1) were lower than those in the western SAZ (2.5 × 1010 viruses l−1 day−1). Viral production in the eastern SAZ (2.2 × 1011 viruses l−1 day−1) was the highest recorded and was approximately one order of magnitude higher than at the other sites. In the western SAZ and PFZ, the percentage of available bacterial biomass lysed by viruses was similar (23.5% and 23% respectively) equating to the release of 3.3 and 2.3 μg carbon l−1 day−1 respectively (assuming a burst size of 50 viruses host−1). In the eastern SAZ the potential bacterial biomass lysed was higher (on average 40%) and corresponded to the release of 26.5 μg carbon l−1 day−1. These findings suggest the importance of the viral shunt in carbon cycling within these regions.